The process of transferring charged toner particles from an image bearing member marking device (e.g. photoreceptor) to an image support substrate (e.g., sheet) involves overcoming cohesive forces holding the toner particles to the image bearing member. The interface between the photoreceptor surface and image support substrate is not always optimal. Thus, problems may be caused in the transfer process when spaces or gaps exist between the developed image and the image support substrate. A critical aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the cohesive forces acting on the toner particles as they rest on the photoreceptive member. Careful control of these electrostatic fields and other forces is required to induce the physical detachment and transfer-over of the charged toner particles without scattering or smearing the developer material. Mechanical devices that force the image support substrate into intimate and substantially uniform contact with the image bearing surface have been incorporated into transfer systems. Various contact blade arrangements have been proposed for sweeping the backside of the image support substrate, with a constant force, at the entrance to the transfer region.
Today, field replacement of a TAB assembly needs to be done in a manner that is very robust and practical, and that meets the specific requirements of the conventional assembly. The TAB assembly has to translate extremely quickly in order to achieve the high speed (e.g., 7 msec) motion necessary to avoid sweeping into the inter-document zone process patches. Therefore, low mass is desirable to prevent the stepper motor from an over torque condition, which leads to skipped “steps”, causing a fault. However, in conventional TAB assemblies, the clamp/post assembly is thick and has an undesirably high mass in order to be rigid enough to support the translation speeds required.
Some spring-type clamps have been attempted but are not practical given that the clamp needs to be structurally supportive (for both the blade and posts), and electrically conductive to the lower semi conductive blade layer. Additionally, such “springs” are typically a thick (˜2.5 mm) sheet metal feature that is sectioned to allow flexure. As such, these springs cannot be compressed enough to provide a biasing force against the blade after riding past the ramp detent (the force is undesirably large and causes a non parallel point contact). In addition, in classical assemblies the upper section of the clamp that biases the blade into the extrusion does not provide a substantially secure and controlled position to maintain a proper 90 degree blade angle.
One known TAB assembly is a high frequency service interval (HFSI) part that has a HFSI replacement life of one million prints. The feature within the TAB assembly that fails or wears out is often a compliant blade subassembly that rides against the backside of the sheet during the Transfer process. This action, over time, even though the blade incorporates an UHMW (ultra high molecular weight) wear layer, eventually renders the blade out of specification for critical design dimensions, ultimately leading to image quality (IQ) defects. The common approach is to replace the entire TAB assembly at one million prints with a new part at a cost of about $80 each.
There is an unmet need in the art for a TAB assembly with a replaceable blade subassembly that can be replaced while the rest of the TAB assembly is retained, thereby reducing replacement costs and waste.